1. Field of the Invention
The present invention relates generally to positioning systems for controlling a dexterous motion of a robot's mechanical degrees of freedom.
2. Background Information
Commercially significant robotic applications evolved from the need to load metalworking Computer Numerically Controlled (CNC) machinery in production environments. The first industrial robots were used for welding, machine loading and tool positioning applications and were adapted to work in well-defined environments where they were required to perform repetitive jobs with a high degree of precision and throughput. Similar CNC approaches are currently used in most advanced robots. All of these robots act according to preprogrammed algorithms and perform reasonably well in well-defined environments. However, CNC approaches, when applied to robots acting in poorly defined real world environments, face many obstacles in achieving cooperative behavior of multiple robots or autopilots for vehicles. It is also problematic to maintain precise positioning and cooperative motion of multiple degrees of mechanical freedom of a single robot, especially as mechanical components age and experience wear.
Most robots utilize one actuator (motor) per single degree of mechanical freedom. Additionally, each degree of mechanical freedom requires at least one high-precision position sensor and, in some cases, a torque monitoring device. Such a torque-monitoring device typically derives its output from the value of a current supplied to the motor's winding, and is thus an indirect sensing mechanism. There are usually no preferred points in the set (if controlled by a stepper motor) or continuum (if controlled by a direct current (DC) motor) of permitted trajectories and, as a result, such systems are plagued by stability problems, which are usually addressed by implementing sophisticated control algorithms. These traditional approaches allow precise and rapid positioning along the pre-calculated trajectory of motion. However, speed, accuracy and stability of motion can be achieved only if all of the components of the motion system behave as specified in accordance with a transfer function defined during the system's programming and subsequent calibration. Additionally, a sophisticated controller is required to perform the motion, which typically increases the cost of such systems. Furthermore, the traditional single-degree-of-freedom control algorithms do not have provisions for integration into systems with multiple degrees of freedom when coherent control of motion of multiple joints of a robot's hand, leg, etc. is desired. The complexity of the controller depends on desired functionality—it can be as simple as digital ON/OFF switch and position limiters or as complex as digital signal processing (DSP)-based solutions with complicated acceleration/deceleration, positioning and contouring algorithms.
For example, a traditional motion-control subsystem becomes prohibitively expensive for any commercial use in a bipedal robot application as, in one form or another, it requires solving, in real time multiple “inverted-pendulum” problems with undefined boundary conditions in real. The problem becomes even more complex when a motion control algorithm is required to account for destabilizing effects associated with movements of adjacent degrees of freedom and/or changes to the robot's center of gravity. It would require taking into account multiple external factors such as the destabilizing effects of rugged terrain and the presence of other moving and/or stationary objects.
Therefore, there is a clear need for a method and device that will allow stable, reliable and inexpensive method for cooperative control of mechanical degrees of freedom of an autonomous robotic device.